Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the velocity of the actuator arm as it seeks from track to track.
When a power failure occurs, it may be desirable to complete pending write commands prior to safely shutting down the disk drive so that user data is not lost. This is of particular concern in disk drives that cache write data in a volatile semiconductor memory prior to writing the data to the disk or a non-volatile semiconductor memory. A conventional disk drive may charge a capacitor to a high voltage using the power supplied by the host, and then use the capacitor voltage to power circuitry in the disk drive to flush a write cache during a power failure. Using a high voltage capacitor to generate the backup power is more cost effective compared to using a lower voltage capacitor or bank of capacitors.